package sym.qrcode.dectector;

import sym.qrcode.NotFoundException;
import sym.qrcode.ResultPoint;
import sym.qrcode.ResultPointCallback;
import sym.qrcode.common.BitMatrix;

import java.util.Vector;

final class AlignmentPatternFinder {

	private final BitMatrix image;
	private final Vector possibleCenters;
	private final int startX;
	private final int startY;
	private final int width;
	private final int height;
	private final float moduleSize;
	private final int[] crossCheckStateCount;
	private final ResultPointCallback resultPointCallback;

	/**
	 * <p>
	 * Creates a finder that will look in a portion of the whole image.
	 * </p>
	 * 
	 * @param image
	 *            image to search
	 * @param startX
	 *            left column from which to start searching
	 * @param startY
	 *            top row from which to start searching
	 * @param width
	 *            width of region to search
	 * @param height
	 *            height of region to search
	 * @param moduleSize
	 *            estimated module size so far
	 */
	AlignmentPatternFinder(BitMatrix image, int startX, int startY, int width,
			int height, float moduleSize,
			ResultPointCallback resultPointCallback) {
		this.image = image;
		this.possibleCenters = new Vector(5);
		this.startX = startX;
		this.startY = startY;
		this.width = width;
		this.height = height;
		this.moduleSize = moduleSize;
		this.crossCheckStateCount = new int[3];
		this.resultPointCallback = resultPointCallback;
	}

	/**
	 * <p>
	 * This method attempts to find the bottom-right alignment pattern in the
	 * image. It is a bit messy since it's pretty performance-critical and so is
	 * written to be fast foremost.
	 * </p>
	 * 
	 * @return {@link AlignmentPattern} if found
	 * @throws NotFoundException
	 *             if not found
	 */
	AlignmentPattern find() throws NotFoundException {
		int startX = this.startX;
		int height = this.height;
		int maxJ = startX + width;
		int middleI = startY + (height >> 1);
		// We are looking for black/white/black modules in 1:1:1 ratio;
		// this tracks the number of black/white/black modules seen so far
		int[] stateCount = new int[3];
		for (int iGen = 0; iGen < height; iGen++) {
			// Search from middle outwards
			int i = middleI
					+ ((iGen & 0x01) == 0 ? ((iGen + 1) >> 1)
							: -((iGen + 1) >> 1));
			stateCount[0] = 0;
			stateCount[1] = 0;
			stateCount[2] = 0;
			int j = startX;
			// Burn off leading white pixels before anything else; if we start
			// in the middle of
			// a white run, it doesn't make sense to count its length, since we
			// don't know if the
			// white run continued to the left of the start point
			while (j < maxJ && !image.get(j, i)) {
				j++;
			}
			int currentState = 0;
			while (j < maxJ) {
				if (image.get(j, i)) {
					// Black pixel
					if (currentState == 1) { // Counting black pixels
						stateCount[currentState]++;
					} else { // Counting white pixels
						if (currentState == 2) { // A winner?
							if (foundPatternCross(stateCount)) { // Yes
								AlignmentPattern confirmed = handlePossibleCenter(
										stateCount, i, j);
								if (confirmed != null) {
									return confirmed;
								}
							}
							stateCount[0] = stateCount[2];
							stateCount[1] = 1;
							stateCount[2] = 0;
							currentState = 1;
						} else {
							stateCount[++currentState]++;
						}
					}
				} else { // White pixel
					if (currentState == 1) { // Counting black pixels
						currentState++;
					}
					stateCount[currentState]++;
				}
				j++;
			}
			if (foundPatternCross(stateCount)) {
				AlignmentPattern confirmed = handlePossibleCenter(stateCount,
						i, maxJ);
				if (confirmed != null) {
					return confirmed;
				}
			}

		}

		// Hmm, nothing we saw was observed and confirmed twice. If we had
		// any guess at all, return it.
		if (!possibleCenters.isEmpty()) {
			return (AlignmentPattern) possibleCenters.elementAt(0);
		}

		throw NotFoundException.getNotFoundInstance();
	}

	/**
	 * Given a count of black/white/black pixels just seen and an end position,
	 * figures the location of the center of this black/white/black run.
	 */
	private static float centerFromEnd(int[] stateCount, int end) {
		return (float) (end - stateCount[2]) - stateCount[1] / 2.0f;
	}

	/**
	 * @param stateCount
	 *            count of black/white/black pixels just read
	 * @return true iff the proportions of the counts is close enough to the
	 *         1/1/1 ratios used by alignment patterns to be considered a match
	 */
	private boolean foundPatternCross(int[] stateCount) {
		float moduleSize = this.moduleSize;
		float maxVariance = moduleSize / 2.0f;
		for (int i = 0; i < 3; i++) {
			if (Math.abs(moduleSize - stateCount[i]) >= maxVariance) {
				return false;
			}
		}
		return true;
	}

	/**
	 * <p>
	 * After a horizontal scan finds a potential alignment pattern, this method
	 * "cross-checks" by scanning down vertically through the center of the
	 * possible alignment pattern to see if the same proportion is detected.
	 * </p>
	 * 
	 * @param startI
	 *            row where an alignment pattern was detected
	 * @param centerJ
	 *            center of the section that appears to cross an alignment
	 *            pattern
	 * @param maxCount
	 *            maximum reasonable number of modules that should be observed
	 *            in any reading state, based on the results of the horizontal
	 *            scan
	 * @return vertical center of alignment pattern, or {@link Float#NaN} if not
	 *         found
	 */
	private float crossCheckVertical(int startI, int centerJ, int maxCount,
			int originalStateCountTotal) {
		BitMatrix image = this.image;

		int maxI = image.getHeight();
		int[] stateCount = crossCheckStateCount;
		stateCount[0] = 0;
		stateCount[1] = 0;
		stateCount[2] = 0;

		// Start counting up from center
		int i = startI;
		while (i >= 0 && image.get(centerJ, i) && stateCount[1] <= maxCount) {
			stateCount[1]++;
			i--;
		}
		// If already too many modules in this state or ran off the edge:
		if (i < 0 || stateCount[1] > maxCount) {
			return Float.NaN;
		}
		while (i >= 0 && !image.get(centerJ, i) && stateCount[0] <= maxCount) {
			stateCount[0]++;
			i--;
		}
		if (stateCount[0] > maxCount) {
			return Float.NaN;
		}

		// Now also count down from center
		i = startI + 1;
		while (i < maxI && image.get(centerJ, i) && stateCount[1] <= maxCount) {
			stateCount[1]++;
			i++;
		}
		if (i == maxI || stateCount[1] > maxCount) {
			return Float.NaN;
		}
		while (i < maxI && !image.get(centerJ, i) && stateCount[2] <= maxCount) {
			stateCount[2]++;
			i++;
		}
		if (stateCount[2] > maxCount) {
			return Float.NaN;
		}

		int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
		if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal) {
			return Float.NaN;
		}

		return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i)
				: Float.NaN;
	}

	/**
	 * <p>
	 * This is called when a horizontal scan finds a possible alignment pattern.
	 * It will cross check with a vertical scan, and if successful, will see if
	 * this pattern had been found on a previous horizontal scan. If so, we
	 * consider it confirmed and conclude we have found the alignment pattern.
	 * </p>
	 * 
	 * @param stateCount
	 *            reading state module counts from horizontal scan
	 * @param i
	 *            row where alignment pattern may be found
	 * @param j
	 *            end of possible alignment pattern in row
	 * @return {@link AlignmentPattern} if we have found the same pattern twice,
	 *         or null if not
	 */
	private AlignmentPattern handlePossibleCenter(int[] stateCount, int i, int j) {
		int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
		float centerJ = centerFromEnd(stateCount, j);
		float centerI = crossCheckVertical(i, (int) centerJ, 2 * stateCount[1],
				stateCountTotal);
		if (!Float.isNaN(centerI)) {
			float estimatedModuleSize = (float) (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;
			int max = possibleCenters.size();
			for (int index = 0; index < max; index++) {
				AlignmentPattern center = (AlignmentPattern) possibleCenters
						.elementAt(index);
				// Look for about the same center and module size:
				if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
					return new AlignmentPattern(centerJ, centerI,
							estimatedModuleSize);
				}
			}
			// Hadn't found this before; save it
			ResultPoint point = new AlignmentPattern(centerJ, centerI,
					estimatedModuleSize);
			possibleCenters.addElement(point);
			if (resultPointCallback != null) {
				resultPointCallback.foundPossibleResultPoint(point);
			}
		}
		return null;
	}

}
